PROJECT SUMMARY Melanin-concentrating hormone (MCH) and hypocretin/orexin (HCRT)-expressing neurons are intermingled populations in the tuberal hypothalamus that project widely throughout the brain to many of the same terminal fields. Whereas the HCRT system has been implicated in the control of wakefulness because the sleep disorder narcolepsy results when these cells degenerate, the HCRT system is also involved in energy metabolism. Conversely, the MCH system has primarily been associated with food intake and energy metabolism, but recent studies have established that MCH neurons also participate in the regulation of sleep and wakefulness. The overarching hypothesis of the Parent R01 grant (R01 NS098813 ?The Tuberal Hypothalamus and Arousal State Control?) is that the HCRT system is wake-stabilizing and REM-inhibiting whereas the MCH system is sleep-facilitating and REM-stabilizing. We will test this hypothesis by determining the phenotype of mice in which either the HCRT neurons, MCH neurons or both cell types have been ablated by removal of doxycycline from the diet of two conditional mouse models, orexin-tTA;TetO DTA mice and MCH-tTA;TetO DTA mice. Professor Yamanaka's lab at Nagoya University has recently created two novel mouse strains that would be quite valuable for us in executing the Aims 1b, 2 and 3 proposed in the Parent R01 grant to test the overarching hypothesis. Specifically, his lab has crossed the orexin-tTA;TetO DTA mice with MCH-tTA mice to create an orexin-tTA;MCH-tTA;TetO DTA mouse strain in which both the orexin and MCH neurons can be conditionally ablated by removal of doxycycline. This strain of double-ablated neuron mice is critical for Aim 1 of ?The Tuberal Hypothalamus and Arousal State Control? to determine whether cataplexy is exacerbated by simultaneously eliminating both neuronal populations. The second novel mouse strain that Professor Yamanaka's lab has generated is a knock-in (KI) mouse in which Flp recombinase is expressed exclusively in the orexin neurons (orexin-Flp mice), which will be extremely valuable for us to address Aims 2 and 3 of NIH R01 NS098813 ?The Tuberal Hypothalamus and Arousal State Control?. An Administrative Supplement from the US-Japan Brain Research Cooperative Program would also enable these two laboratories to establish collaboration on a new topic: investigation of the role of MCH neurons in memory consolidation during sleep. Together, these experiments should provide a more complete picture of the interaction of the HCRT and MCH neuronal populations, the consequences of simultaneous loss of these cells, and the hypothetical role of MCH neurons in memory.